Electric motor follow-up system



Aug. 31, 1948. w. H. NEWELL ETAL 2,448,387

ELECTRIC MOTOR FOLLOW-UP SYSTEM Filed April 23, 1946 2 Sheets-Sheet 1 3 Y NE E Tam N N W R E 0 h VMF. T m w 3 m om w om wm 6 $6 $0 m H7 J Qt Hi e o3 g m? n" E v f5 ,3" RH ow mm h o a 2 mm m: o W- mal w an @m E lav. 03 mw 5% Aug. 31, 1948. w. H. NEWELL ETAL 2,443,387

ELECTRIC MOTOR FOLLOW-UP SYSTEM 2 SheetsSheet 2 Filed April 23, 1946 mm m m IIII 1:. W 00 Nv E E MN.

7M ATTO RNEY Patented Aug. 31, 1948 UNITED STATES PATENT OFFICE ELECTRIC MOTOR FOLLOW-UP SYSTEM Application April 23, 1946, Serial No. 664,206

1 Claim. -(Cl. 318--30) v This invention relates to motion reproducing units and more particularly to a unit involving an electrically driven prime mover which is connected to respond to a position indicating signal in an electrical synchroreceiver.

The present invention is applied to a synchroreceiver of the type having a rotor in which a voltage is induced which is dependent upon its angular position relative to the position of the rotor of a remote synchro-transmitter. When the rotor is in correspondence with the rotor of the transmitter a zero voltage is produced. When the rotor is out of correspondence a plus or minus voltage is produced depending upon the direction and angular extent of the error. The present invention provides an electrical channel responsive to the error voltage produced in the synchro rotor and connected to drive a motor in a direction to bring the rotor to zero voltage position.

It is an object of the invention to provide a novel and improved system of the above type.

Another object is to provide a system of the above type in which the motor is caused to follow accurately the incoming signals without hunting or overrunning.

Another object is to provide a system of the above type having novel and improved details of construction and features of operation.

Various other objects and advantages will be apparent as the nature of the invention is more fully disclosed.

The present system utilizes a pair of receiving units connected for coarse and fine control respectively. The units may for example be interconnected to drive at a 36 to 1 ratio so that the fine control unit makes a complete revolution for each movement of the coarse control unit. The system is so arranged that the driving mbtor is normally under control of the fine control unit. However, when the error exceeds a predetermined angular amount on the coarse control unit, the coarse receiver takes control and retains control until the error is again reduced to this predetermined amount. The point at which the coarse control takes effect is selected to prevent the fine control from synchronizing in its 180 or reverse position, and preferably takes effect at the maximum voltage position of the fine control element. For example with a 36 to 1 ratio as above specified the maximum voltage position of the fine unit would correspond to 2/2 on the coarse control unit. Hence the system may be arranged so that the coarse control takes over whenever the error exceeds 2/z plus or minus.

In a system of the above type there would normally be a possibility that the coarse control unit would synchronize in its or reverse position. In order to avoid this contingency an offsetting voltage is introduced which offsets the reverse zero voltage position of the coarse control unit from its 180 point by an amount such that the zero voltage position of the fine control unit will not coincide with the zero voltage position of the coarse control unit at its reverse position. In the example given above the offset voltage may be so selected as to oilset the reverse zero voltage position on the coarse control unit by about 2 from the 180 point. This position would then correspond to a maximum voltage position on the fine control unit and the two units would not both reach zero voltage position at other than their correct forward synchronized position.

Another feature of the invention involves converting the control voltage, which is normally proportional to the angular error, into a substantially constant voltage suited to produce maximum torque on the drive motor over a wide range of angular error. The drive motor is thus able to operate at maximum efliciency for bringing the receiver into exact registration with the incoming signal.

The control voltage of course decreases to zero and reverses when the zero position is approached and passed. In order to obtain maximum driving power throughout a large portion of the angular range without causing the motor to overrun and hunt a braking voltage is introduced which is proportional either to the acceleration or the rate of change of acceleration of the driving motor, and introduces a braking effect which is adapted to bring the motor to rest at the zero voltage position without overrunning, The control voltage is preferably proportional to the second derivative of the rate of the driving motor which corresponds to rate of change of acceleration.

The invention also includes a novel means for obtaining an A. C. voltage which is proportional to a derivative of the rate of drive. For this purpose an alternating voltage is produced having an amplitude proportional to the rate of drive of the driving motor. This alternating voltage is converted into a D. C. voltage which is likewise proportional to the rate of drive. The D. C. voltage is differentiated twice by a differentiating network to obtain a voltage which is proportional to the second derivative of the rate of drive, that is to the rate of change of acceleration. This latter D. C. voltage is then reconverted to an alternating voltage which is likewise proportional to the rate of change of acceleration and is in phase 3 with the voltage from the fine receiver with which it is combined for controlling the driving motor.

Although the novel features which are believed to be characteristic of the invention are pointed out more particularly in the. claim appended hereto, the nature of the invention will be better understood by referring to the following description taken in connection with the accompanying drawings in which a specific embodiment thereof is set forth for purposes of illustration.

In the drawings:

Figs. 1 and 2 placed side by side constitute a schematic diagram of a. system embodying the present invention.

Referring to the drawings more in detail, the incoming signal on lines In and II is fed to the stators I2 and I3 of synchro receivers I4 and I5 respectively having rotors I6 and I I which are arranged to be positioned by a drive shaft I8 through gears I9 and respectively. The gears I 8 and 20 are so arranged that the rotor Il makes several complete revolutions for each revolution of the rotor I6. For example, the rotor I'I may make 36 revolutions for each revolution of the rotor I6. 7

The synchro receivers I4 and I 5 are of the usual construction and are arranged so that the voltage in the rotors I6 and I1 vary as a function of the angular displacement of the rotors from the positions of corresponding rotors in the remote synchro transmitters from which the incoming signal is received. When the rotors are in correspondence with the positions of the transmitters a zero voltage is induced therein from the stators I2 and I3.

In the embodiment shown the voltage induced in the rotor I1 is supplied by a line and resistor 26 to the input circuit of an amplifier tube 21. The resistor 26 is provided with a variable tap 28 so that the voltage applied to the amplifier 21 may be adjusted as desired. This voltage constitutes the A. C. voltage induced in the rotor I! and corresponds to the error in position of the fine adjustment receiver I5. The output voltage from the amplifier 2'! is fed through resistor 38 and line- 3| to a combining network comprising a condenser 32 and resistors 33 and 36. The resistor 36 is connected by a line 34 across to the input circuit of an amplifier tube 35. The resistors 33 and 36 which may be of the order of 1 megohm each constitute in efiect a voltage divider network.

The output; of the amplifier tube is connected by a line 48 through condenser 4| and resistors 42 and 43 to the input circuit of an amplifier tube 44. The output circuit of the amplifier tube 44 is supplied through a condenser 45 and a line 46 to the input circuit of an amplifier tube 58. The input circuit of the amplifier tube 50 is connected to ground through a pair of resistors 5| and a resistor 52 connected in series. A resistor 53 is connected between the cathode of the tube 58 and ground to provide a bias voltage. The common point 54 of the resistors 5| is connected by a line 55 to the grid 56 of an amplifier tube 51. The output circuit of the amplifier tube 51 is connected through condenser 58 and line 59 to the input of an amplifier tube 60. Resistors 6| are connected between the line 59 and the resistor 52 and form with the resistors 5|, a balancing network.

It will be noted that the output voltage of the amplifier tube 44 is greater than the input voltage amplifier 44 and hence is of the same value as the input voltage to the amplifier tube 44, but difi'ers in phase by 180 from the input voltage to the tube 44. The amplifier tube 51 again reverses the phase of its output current so that the output of the tube 51 is 180 displaced in phase from the output from the tube 44. The above described connections are such that the tubes 44 and 51 are caused to operate as push-pull amplifiers. The resistance network including resistors 5|, 6|, and 52 are used to cause push-pull operation of the tubes 44 and 51 and could, of course, be replaced by the push-pull input transformer to the tubes 44 and 51. The resistance network however is more compact and provides a more faithful reproduction of the input signal.

The tubes 50 and 68 which are supplied respectively by the tubes 44 and 51 likewise constitute push-pull amplifiers. For increased power a second pair of tubes 58a and a are connected in parallel with the tubes 58 and 68 respectively. The input circuit of the tubes 50a and 80a being connected to the lines 46 and 59 respectively by lines 46a and 59a and resistors 52 and 63. The output circuits of the tubes 50 and 60a are connected by lines to a split primary of an output transformer 61. The output circuit of the tubes 60 and 60a is connected through a line 68 to the split primary 66. The primary winding 88 may be tuned by condensers 68 to the fundamental frequency of the applied voltage so as to eliminate or reduce the harmonics and extraneous voltages. The output transformer 61 is provided with a pair of secondaries 10 and II. The secondary I0 is connected through a resistor 12 to ground and a point 13 of the resistor I2 is connected by a line I4 and a resistor I5 to the input side of the tube 44 to constitute a negative feedback which eliminates or suppresses the distortion or pickup voltages which may be produced by the operation of the amplifiers. The secondary II constitutes the output secondary and is'connected by leads 88 to supply power to a reversible drive motor 8| which is connected to drive the shaft I8. The field of the drive motor 8| is supplied from a volt A. C. line 82 by a line 83. The connections of the lines 80 to the drive motor 8| is such that the drive motor is caused to rotate in a direction'to bring the rotor I! to zero voltage position.

The rotor I5 of the coarse receiver is connected by a line 85 to the input circuit of an amplifier tube 86. The output circuit of the amplifier tube 86 is connected through a condenser 81 and resistor 88 to ground and through condenser 81 and a gas tube 89 to the input line .34 to the amplifier tube 35 at a point between the resistors 33 and 36. The arrangement is such that the gas tube 89 is normally inoperative and prevents any voltage from being supplied from the tube 86 to the input of the tube 35. However, a voltage is developed by the tube 86 which as pointed out above is proportional to the error in the position of the rotor I6. The connection is such that when this voltage exceeds a predetermined value corresponding to a predetermined angular error. the gas tube 89 becomes conductive and allows the voltage from the tube 88 to be supplied to the input of th amplifier tube 35. The tube 86 thus becomes a low resistance path in parallel to the h h resistance 36 and thus eliminates the effect 5- of any incoming voltage'from the fine receiver on the amplifier 35 and subsequent elements of the circuit. The amplifier 35 is then virtually under the control of the amplifier 86 and the succeeding portions of the circuit respond to the signal from the coarse receiver I4 instead of to signals from the fine receiver I5.

In order to ofiset the reverse zero position of the rotor I 6 from its 180 point for the purpose above mentioned the rotor I6 is connected by a line 90 to a point 9| in a resistor network comprising resistors 92, thence to ground. The resistors 92 are connected through a condenser 93 and line 94 to a secondary 95 of a transformer 96 having a primary 91 connected to the A. C. line 82. The value of the offsetting voltage is determined by the position of the point 9I with respect to the resistors 92 and is so selected that the offsetting voltage corresponds to about 90 on the fine rotor I1 which in the example chosen, namely 36 to 1 ratio, constitutes 2 /2 degrees movement of the coarse rotor I6. It is noted that this offsetting voltage is introduced into the rotor I6 in series with the voltage induced from the stator I 2 of the receiver I4. The condenser 93 is a phasing condenser to bring the ofisetting voltage into phase with the error voltage in the rotor IS. The rotor I6 is of course so positioned with respect to the shaft I8 that its zero voltage position in a forward direction corresponds to the zero voltage position of the rotor I1, whereas its zero voltage position in the reverse direction is ofiset from the 180 point by an amount determined by the value of the ofisetting voltage from the resistors 92 as above mentioned.

In order to obtain a braking voltage for the purpose referred to above an induction generator I is connected to be driven by the shaft" I8. The field of the generator I00 is supplied by lines IOI with 115 v. from the A. C. line 82 through a phasing condenser I02 which is designed to make the output voltage in phase with the voltage of the A. C. line 82. The output of the induction generator is supplied by a line I03 to a bridge circuit comprising a pair of resistors I04 and I05 connected in series. One end of resistor I04 is connected to the cathode of a rectifier tube I06, the anode of which is connected to a winding I01 constituting a secondary of the transformer 90. resistor I05 is connected to the anode of a rectifier tube I08, the cathode of which is connected by a line I09 to a winding |I0 likewise constituting a secondary of the transformer 96. The windings I I0 and I01 are connected together at III. The point III is grounded through a condenser II2. It will be noted that the resistors I04 and I05, rectifiers I06 and I08 and windings I01 and I I I0 are connected in series circuits so that current fiows therethrough in the direction of the arrows H3. The line I03 is connected to the common point N4 of the resistors I04 and I05. The elements are so chosen that with current flowing through the circuits derived from the secondaries I01 and H0, the points III and H4 are of equal potential, and no voltage is applied to the condenser I I2. However, when voltage is supplied to the point II 4 by the line I03 the current flowing through the respective halves of the bridge circuit including tubes I05 and I08 becomes unbalanced and a voltage appears across the condenser 2. This voltage across the condenser H2 is in the form of D. C. voltage which is proportional to the A. C. voltage supplied to the point H4. The bridge circuit including the tubes I06 and I08, resistors I04, I05, secondaries I01 and H0 ac- The,

- voltage applied by the line I03.

cordingly convert the applied A. C. voltage to a proportional D. C. voltage.

The high voltage side of the condenser H2 is connected to ground through a condenser I20 and a resistor I2I. The condenser II2 discharges through the condenser I20,and the resistor I2I at a rate to maintain equilibrium. When the voltage on the condenser H2 is constant, there will be no current flow through the resistor I2I except for the negligible leakage current. When, however, the voltage across the condenser I I2 changes the condenser discharges in a succession of discharges through the condenser I20 and resistor I2I until equilibrium is again established. Consequently the current through the resistance I2I corresponds to the rate of change of the A. C. Since the voltage supplied by the generator I00 is proportional to the rate or velocity of the shaft I8, the voltage developed across the resistor I2I corresponds to the derivative of the velocity oracceleration.

The condenser I20 is in turn connected through the condenser I22 and a resistor I23 to ground. The condenser I22 and resistor I23 act in a manner similar to the condenser I20 and resistor I2I to develop a voltage across the resistor I23 which is proportional to the rate of change of voltage across the resistor I2I This voltage accordingly is proportional to the rate of change in velocity or to the second derivative of the velocity of the shaft I8. The resistor I23 may be replaced or supplemented by a condenser I23a if desired.

In order to convert this D. C. voltage which represents the second derivative of velocity to a corresponding alternating voltage,'a bridge network is provided which comprises tubes I25 and I26, secondaries I21 and I28 and resistor network including resistors I30, connected in series circuit so that current will fiow through the circuit in the direction of the arrow I3I in response to voltage induced in the secondary coils I21 and I28. The resistor I23 is connected between a point I32 between the secondaries I21 and I28 and ground, adjustable tap I33 on the resistors I30 is grounded through a resistor I34. A resistor network including resistors I35, I36 and I31 is connected across the resistors I30 and an adjustable tap on the resistor I31 isconnected to ground.

A resistor network including resistors I40, MI and I42 is connected across windings I21 and I28 and an adjustable tap I43 on the resistor I4I is connected to ground. The adjustable tap I33 of the resistor I30 is connected by a line I45 to the input circuit of an amplifier tube I46, the output circuit of which is connected through a resisis balanced and no voltage appears across the resistor I34. However, when a-D. C. voltage is applied to the resistor I23 this balance is upset with the result that an 'A. C. voltage appears across the resistor I34 which is proportional to the D. C. voltage supplied to the resistor I23. This A. C. volt e appearing across the resistor I34 is supplied o the amplifier tube I46 and thence to the combining network to be combined with the control voltage. This alternating voltage. which is in phase with the control voltage and is proportional to the second derivative of the velocity of the shaft I8, is introduced into the system in a sense to introduce a braking effect on the drive motor which tends to bring the same to rest. Due to the fact that this voltage is proportional to the rate of change of acceleration of the drive motor it appears only in that portion of the cycle of operation during which the drive motor is accelerating or decelerating as it approaches its zero position.

As pointed out above the voltage applied to the amplifier 35 is proportional to the angle of error of either the fine control receiver or the coarse control receiver. As the zero position is approached the fine control receiver is in control. The amplifiers are so designed that when the voltage supplied by the rotor H of the fine receiver is less than a predetermined value the amplifier output voltage is proportional to the i applied voltage. When, however, the input voltage exceeds this predetermined value the amplifier output voltage remains constant, but is converted to a square wave form. The power amplifier system is so designed that this square wave voltage will represent full voltage for the driving motor, for example 115 volts, so that full voltage is supplied thereto throughout the constant voltage area. In one embodiment for example the rotor l'l may develop a half of volt for push-pull amplifier stages described above to supply 115 volts to the driving motor 98. In this way a full torque is produced by the driving metor throughout its entire range of movement beyond a plus or minus two minute error and the acceleration and deceleration must take place during this plus or minus two minute movement. The braking elfect of the second derivative voltage derived from the induction generator M0 through the bridge networks above described is accordingly utilized to introduce a braking effeet which is proportional to the rate of change of acceleration and is designed to bring the motor to rest within this relatively short plus or minus two minute error range during which the control voltage is proportional to velocity.

The amplification factor of the amplifiers is limited by the efiect of the voltage at zero position of the fine adjustment rotor which may be of the order of 0.1 volt and consists of torque producing harmonics and quadrature cycle components which would tend to overload the amplifier but produce no torque. In the above described system an over-all amplification-factor of 1 to has been assumed. The constant voltage range of the system should be as long as possible in order to maintain maximum driving efiiciency of the motor. However, the constant voltage range is limited by the minimum angular range within which the motor can be brought to rest without over-shooting to the opposite constant voltage area.

Although a specific embodiment of the invention has been shown for purposes of illustration, it is to be understood that system and component parts thereof are capable of various uses and that the scope of the invention is only to be restricted in accordance with the following claim.

What is claimed is:

In an electric follow-up system, a pair of receivers having field windings carrying the received position signal and having rotors in which a voltage is induced which is a function of their angular displacement from a zero voltage position corresponding to the received position signal, said rotors being coupled to rotate at different rates to constitute coarse and fine control rotors, respectively, a driving motor for said rotors, an electric control channel for said motor including amplifiers, means supplying a control voltage to said channel from said fine control rotor suited to drive said rotor to zero voltage position, and a circuit to supply a control voltage to said channel from said coarse control rotor, said circuit including an amplifier tube having an input circuit connected directly to said coarse con-trol rotor and having an anode circuit connected to said channel and a gas tube connected in said anode circuit to isolate said coarse control means from said channel, said tube being arranged to become conductive only when the control voltage from said last rotor exceeds a value representing a predetermined error in position.

WDZLIAM H. NEWELL. HENRY F. MCKENNEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,233,415 Hull Mar. 4, 1941 2,376,359 'Hul-tin May 22, 1945 2,407,876 Godet Sept. 17, 1946 2,409,97'0 Agins Oct. 22, 1946 2,411,573 Holst et al Nov. 26, 1946 

